Internally oxidized silver-cadmium oxide has been in wide use as a material for silver-metal oxide alloy electrical contacts, but with recent concern over the potential hazard of cadmium, Ag-SnO.sub.2 -In.sub.2 O.sub.3 -CdO contacts have come to be used in medium-load breakers. Ag-SnO.sub.2 -In.sub.2 O.sub.3 -CdO materials are produced by internal oxidation of Ag-Sn-In-Cd alloys, and when used in medium-load breakers, they exhibit more resistance to sticking and wear less than Ag-CdO, and at the same time, their weight is as much as 30% less than that of Ag-CdO, thus making a great contribution to silver saving. But the conventional Ag-SnO.sub.2 -In.sub.2 O.sub.3 -CdO contact has one serious problem; mud-cracking develops in the contact surface and cause its partial dislodging. Analysis has shown that this defect is caused by arc current that flows through Ag-rich large grain boundaries in the Ag-SnO.sub.2 -In.sub.2 O.sub.3 -CdO formed as a result of internal oxidation.